[R-pkg-devel] Strange Additional_repositories NOTE followed by package install error

I am unable to reproduce a recent R CMD check failure on CRAN
concerning a package of mine: grattan.

This package Suggests: taxstats which is a large package hosted by an
Additional repository: https://hughparsonage.github.io/drat/

When I run this check locally, on travis, and on appveyor with
_R_CHECK_CRAN_INCOMING_ = true I get the expected NOTE:


* checking CRAN incoming feasibility ... NOTE
Maintainer: ?Hugh Parsonage <hugh.parsonage at gmail.com>?
Suggests or Enhances not in mainstream repositories:
   taxstats
Availability using Additional_repositories specification:
taxstats   yes   https://hughparsonage.github.io/drat/


However, on CRAN (including win-builder) I get the rather curious NOTE:

* checking CRAN incoming feasibility ... NOTE
Maintainer: 'Hugh Parsonage <hugh.parsonage at gmail.com>'

Suggests or Enhances not in mainstream repositories:
   taxstats
Availability using Additional_repositories specification:
   taxstats   no   ?
   ?           ?   https://hughparsonage.github.io/drat/
Additional repositories with no packages:
   https://hughparsonage.github.io/drat/


followed by errors resulting from failures to install 'taxstats' when
code such as the following is run to re-build vignettes:

if (requireNamespace("taxstats", quietly = TRUE)){
   library(taxstats)
} else {
   templib <- tempfile()
   hutils::provide.dir(templib)
   install.packages("taxstats",
                    lib = templib,
                    repos = "https://hughparsonage.github.io/drat/",
                    type = "source")
   library("taxstats", lib.loc = templib)
}


Since the failures only occur on Windows machines, and have only
appeared recently, I have considered modifying the DESCRIPTION file to
'trick' win-builder into reinstalling taxstats, as I suspect there may
be caching issues. However, given that the 'taxstats' package takes a
fairly long time to install, I don't want to do this nor submit to
CRAN in case I am missing something else that's causing the check to
fail.